freeCodeCamp/curriculum/challenges/chinese/02-javascript-algorithms-and-data-structures/basic-javascript/replacing-if-else-chains-with-switch.md

id, title, challengeType, videoUrl, forumTopicId, dashedName

id	title	challengeType	videoUrl	forumTopicId	dashedName
56533eb9ac21ba0edf2244e0	用一个 Switch 语句来替代多个 if else 语句	1	https://scrimba.com/c/c3JE8fy	18266	replacing-if-else-chains-with-switch

--description--

如果你有多个选项需要选择，switch语句写起来会比多个串联的if/if else语句容易些，譬如:

if (val === 1) {
  answer = "a";
} else if (val === 2) {
  answer = "b";
} else {
  answer = "c";
}

可以被下面替代：

switch(val) {
  case 1:
    answer = "a";
    break;
  case 2:
    answer = "b";
    break;
  default:
    answer = "c";
}

--instructions--

把串联的if/if else语句改成switch语句。

--hints--

不要使用else表达式。

assert(!/else/g.test(code));

不要使用if表达式。

assert(!/if/g.test(code));

你应该有至少 4 个break表达式。

assert(code.match(/break/g).length >= 4);

chainToSwitch("bob")应该为 "Marley"。

assert(chainToSwitch('bob') === 'Marley');

chainToSwitch(42)应该为 "The Answer"。

assert(chainToSwitch(42) === 'The Answer');

chainToSwitch(1)应该为 "There is no

assert(chainToSwitch(1) === 'There is no #1');

chainToSwitch(99)应该为 "Missed me by this much!"。

assert(chainToSwitch(99) === 'Missed me by this much!');

chainToSwitch(7)应该为 "Ate Nine"。

assert(chainToSwitch(7) === 'Ate Nine');

chainToSwitch("John")应该为 "" (empty string)。

assert(chainToSwitch('John') === '');

chainToSwitch(156)应该为 "" (empty string)。

assert(chainToSwitch(156) === '');

--seed--

--seed-contents--

function chainToSwitch(val) {
  var answer = "";
  // Only change code below this line

  if (val === "bob") {
    answer = "Marley";
  } else if (val === 42) {
    answer = "The Answer";
  } else if (val === 1) {
    answer = "There is no #1";
  } else if (val === 99) {
    answer = "Missed me by this much!";
  } else if (val === 7) {
    answer = "Ate Nine";
  }

  // Only change code above this line
  return answer;
}

chainToSwitch(7);

--solutions--

function chainToSwitch(val) {
  var answer = "";

  switch(val) {
    case "bob":
      answer = "Marley";
      break;
    case 42:
      answer = "The Answer";
      break;
    case 1:
      answer = "There is no #1";
      break;
    case 99:
      answer = "Missed me by this much!";
      break;
    case 7:
      answer = "Ate Nine";
  }
  return answer;
}